THE PARALLEL ROADS OF GLEN ROY. 221 



by the frozen material above, and their consumption in 

 the milder air below. For a period supply exceeded 

 consumption, and the ice extended, filling Glen Spean 

 to an ever-increasing height, and abutting against the 

 mountains to the north of that glen. But why, it may 

 be asked, should the valleys south of Glen Spean be 

 receptacles of ice at a time when those north of it were 

 receptacles of water? The answer is to be found in 

 the position and the greater elevation of the mountains 

 south of Glen Spean. They first received the loads of 

 moisture carried by the Atlantic winds, and not until 

 they had been in part dried, and also warmed by the 

 liberation of their latent heat, did these winds touch 

 the hills north of the Glen. 



An instructive observation bearing upon this point 

 is here to be noted. Had our visit been in the winter 

 we should have found all the mountains covered; had 

 it been in the summer we should have found the snow 

 all gone. But happily it was at a season when the 

 aspect of the mountains north and south of Glen Spean 

 exhibited their relative powers as snow collectors. 

 Scanning the former hills from many points of view, 

 we were hardly able to detect a fleck of snow, while 

 heavy swaths and patches loaded the latter. Were the 

 glacial epoch to return, the relation indicated by this 

 observation would cause Glen Spean to be filled with 

 glaciers from the south, while the hills and valleys on 

 the north, visited by warmer and drier winds, would 

 remain comparatively free from ice. This flow from 

 the south would be reinforced from the west, and as 

 long as the supply was in excess of the consumption 

 the glaciers would extend, the dams which closed the 

 glens increasing in height. By-and-by supply and con- 

 sumption becoming approximately equal, the height of 

 the glacier barriers would remain constant. Then, if 



